Buckwheat (Fagopyrum ssp.) is an ancient crop belonging to Fagopyrum Mill, Polygonaceae family, which has been widely cultivated around the world, especially in East Asia and East Europe. Buckwheat is the major food crop in the high-attitude regions, including the Liangshan region of China for thousands of years. Buckwheat is rich in nutrition and considered as a functional food for the high contents of rutin and other bioactive compounds that are antioxidant and anti-tumor. Two species of cultivated buckwheat, common buckwheat (Fagopyrum esculentum) and tartary buckwheat (Fagopyrum tataricum), are widely spread, while the wild buckwheat resources only distribute in some certain regions. Southwest China, including Sichuan, Yunnan, Guizhou Province and Tibet Autonomous Region, is widely known as the center of origin, distribution and diversity of wild buckwheat plants. So far, more than 20 buckwheat species have been named and classified, most of which have been found in Southwest China. The extremely complicated geographical environment of this area renders a number of diversified wild buckwheat resources. However, the scientific classification of Fagopyrum Mill species is deficient, and some wild species are synonyms. Since 2004, our research team continually made field investigation and specimens collection works in Southwest China, anatomic observation of flowers and fruits were also made in our lab. Based on these morphological data as well as buckwheat chromosome number detecting results, comparing with other specimens, model photos and pervious articles, the Fagopyrum Mill was taxonomic revised and the number of species were adjusted from 28 to 21, namely, Fagopyrum megaspartanium Q. F. Chen and F. pilus Q. F. Chen were treated as synonyms of F. cymosum (Trrev)Meisn; F. pleioramosum Ohnishi and F. wenchuanense J.R.Shao were treated as synonyms of F. caudatum (Samuelsson) A. J. Li; F. callianthum Ohnishi was treated as a synonym of F. qiangcai D.Q.Bai; F. zuogongense Q.F.Chen was treated as a synonym of F. homotropicum Ohnishi; F. longzhoushanense J.R.Shao was treated as a synonym of F. pugense T.Yu. The key to species of Fagopyrum were also revised and presented. Our results provided a better understanding of the evolution position of Fagopyrum Mill and built a framework to learn the genetic relationships between buckwheat species.